(1.) Field of the Invention
The present invention relates to a solid-state imaging device and a camera.
(2.) Description of the Related Art
A conventional solid-state imaging device obtains signals of desired colors through color filters in order to obtain pixel signals which correspond to red (R), green (G) and blue (B). Incident light which enters the solid-state imaging device enters photodiodes via microlenses and color filters. An example of an arrangement of is color filters is the Bayer arrangement.
A conventional technology of a solid-state imaging device which enhances sensitivity and improves a color separating characteristic is disclosed in the Japanese Laid-Open Patent Application No. 2000-151933 (Patent Reference 1).
FIG. 1 is a plan view showing an imaging element of the above mentioned conventional technology. FIG. 2 is a cross-section diagram taken along the line A-A′ in FIG. 1.
The solid-state imaging device shown in FIG. 2 includes a red photodiode 2, a green photodiode 3, and a blue photodiode 4 which are positioned near a surface of a semiconductor substrate 1. The red photodiode 2, the green photodiode 3, and the blue photodiode 4 are covered by a transparent film 5 which is made of silica glass, for example.
The transparent film 5 is formed in such manner that its top surface, opposite to its lower surface covering the photodiodes 2, 3 and 4, has a mountain range-like shape. A filter 6, a filter 7 and a filter 8 are formed on inclined areas of the top surface of the transparent film 5 having the mountain range-like shape which are inclined by a fixed angle in the same direction. The filters 6, 7 and 8 are arranged in positions which correspond to the photodiodes 2, 3 and 4, respectively.
The inclination angle of each of the filters 6, 7 and 8 is preferred to be as close to 45° as possible so that light which enters the filter 6 from above is reflected towards the right direction of the figure, and is then reflected by the filter 7 or 8 to enter the photodiode 3 or 4, respectively.
The filter 6 has a characteristic that allows transmission of red light R and reflects green light G and blue light B. The filter 7 has a characteristic that allows transmission of blue light B and reflects green light G. The filter 8 has a characteristic that reflects any colors of light.
The filters 6 and 7 generally include a multilayer film which is called dichroic filter, and are structured in the same manner as the filter which is usually formed on a surface of a dichroic prism of a three charge coupled device (3CCD) video camera and an electric still camera. The filter 8 includes a total reflection film which includes a metal film made of aluminum, for example.
The filters 6, 7 and 8 are covered by a transparent film 9 having a refractive index which is low compared to that of the transparent film 5.
On an area of the transparent film 9 that corresponds to the filter 6, there is a concave lens 11. The transparent film 9 is covered by a light-blocking film 35. On an area of the light-blocking film 35 that corresponds to the filter 6, there is an aperture 36. Through the aperture 36 of the light-blocking film 35 and the concave lens 11, light enters the filter 6 only, and unnecessary light does not enter the other filters 7 and 8 as the unnecessary light is blocked by the light-blocking film 35.
The light-blocking film 35 and the concave lens 11 are covered by a transparent film 12. On an area of the transparent film 12 that corresponds to the filter 6, there is a convex lens 13. Accordingly, for a set of one red photodiode 2, one green photodiode 3, and one blue photodiode 4 for three pixels, there is a light condenser which is made up of a pair of one convex lens 13 and one concave lens 11.
Incident light is condensed by the convex lens 13 and the concave lens 11, and enters, as collimated light, the filter 6 which is an initial stage.
Among the incident light which enters the filter 6, red light R enters the red photodiode 2 through the filter 6. Among the incident light which enters the filter 6, green light G and blue light B are reflected by the filter 6 towards the right direction, that is, towards the filter 7.
Green light G and blue light B enter the filter 7. However, green light G is reflected by the surface of the filter 7, and enters the green photodiode 3. Blue light B transmits the filter 7 and enters the filter 8. Then blue light B is reflected by the filter 8 and enters the blue photodiode 4.
As described above, the solid-state imaging device of the conventional technology: separates the incident light into red, green and blue as the filters 6, 7 and 8 reflect and/or allow transmission of the incident light; and allocates the light of each color to the corresponding photodiode 2, 3 or 4. As a result, compared to filters having a structure in which specific light among incident light is thermally converted and the remaining light passes, the percentage of the incident light which reaches the photodiodes increases and thus the sensitivity is enhanced.
However, as pixel cells in solid-state imaging devices of recent years become denser and minitualized, the sensitivity is desired to be further enhanced. For example, in the above described conventional technology, separating primary colors from incident light results in a loss of light when light of each primary color transmits or reflects off. For example, in FIG. 2, blue light B reflects off the filter 6, transmits the filter 7, and reflects off the filter 8, and thus causing a loss of light.
The present invention aims at providing a solid-state imaging device and a camera which can enhance a resolution and sensitivity.